The present invention relates to a cathode ray tube apparatus used in a monitor of an electronic computer or a television receiver and to a deflection device for a cathode ray tube.
In general, a cathode ray tube apparatus comprises a cathode ray tube and a truncated cone-shaped deflection device mounted on the cathode ray tube. The cathode ray tube comprises a vacuum envelope having a face panel and a funnel. A phosphor screen is formed on the inner surface of the face panel, and an electron gun is arranged within the funnel. On the other hand, the deflection device comprises deflection coils mounted on the outer circumferential surface of the funnel for deflecting the electron beams emitted from the electron gun in the horizontal and vertical directions, respectively, a core arranged in the vicinity of the deflection coils, and a correcting coil for rotating the displayed picture image about the tube axis.
In the cathode ray tube apparatus of the particular construction, a positional deviation in the rotating direction about the tube axis tends to take place when the deflection device is assembled on the vacuum envelope of the cathode ray tube. In order to correct the positional deviation in the rotating direction, the deflection device is provided with the correcting coil such as a rotation coil, a tilt coil or a Z coil, and a DC current is allowed to flow through the correcting coil so as to correct the positional deviation in the rotating direction.
In general, the correcting coil is arranged in an open end portion of the deflecting device on the side of a phosphor screen. In addition to the deflection of the electron beams performed by the vertical and horizontal deflection coils of the deflection device, an auxiliary deflection of the electron beams is performed by the magnetic field produced by the correcting coil so as to correct the positional deviation of the displayed image about the tube axis. Of course, it is desirable for the correcting coil to be arranged as close to the tube axis as possible.
In the conventional cathode ray tube apparatus, the correcting coil is shaped substantially circular like the cross sectional shape of the deflection device-mounting portion of the funnel and the cross sectional shape of the open end portion of the deflection device on the side of the phosphor screen.
However, in recent years, the cross section of the yoke-mounting portion of the vacuum envelope of the cathode ray tube is not limited to a circular cross section, and the cross section is also shaped rectangular or elliptical. In this connection, the horizontal and vertical coils of the deflection device and the core are also shaped to have a rectangular or elliptical cross section.
Where a conventional correcting coil having a circular cross section is used in such a cathode ray tube apparatus, it is difficult to arrange the correcting coil close to the tube axis of the cathode ray tube. It follows that it is difficult for the correcting coil to correct efficiently a positional deviation of the displayed image.
The present invention has been contrived in consideration of the above described circumstances and its object is to provide a cathode ray tube apparatus that permits efficiently correcting a positional deviation of the displayed image in the rotating direction about the tube axis to obtain desired displayed image characteristics and to provide a deflecting device for a cathode ray tube.
According to an aspect of the present invention, there is provided a cathode ray tube apparatus, comprising:
a cathode ray tube including an envelope having a face panel on an inner surface of which a phosphor screen is formed and a funnel joined to the face panel, and an electron gun arranged within a neck of the funnel for emitting electron beams toward the phosphor screen; and
a substantially funnel-shaped deflection device having a first open end on the side of the phosphor screen and a second open end on the side of the neck and mounted on the outer circumferential surface of a deflection device-mounting section of the funnel.
The deflection device includes a substantially funnel-shaped core, a plurality of deflection coils for deflecting the electron beams in the horizontal and vertical directions, and a correcting coil provided at the first open end for rotating a displayed image about the tube axis. The correcting coil is shaped non-circular, which is substantially equal to the shape of the first open end of the deflection device.
In the present invention, the deflection device-mounting section of the funnel has a substantially rectangular cross section. Also, the first open end of the deflection device and the correcting coil are shaped substantially rectangular to conform with the cross section of the deflection device-mounting section.
Moreover, according to the present invention, the deflection device-mounting section of the funnel has a substantially elliptical cross section. Also, the first open end of the deflection device and the correcting coil are shaped substantially elliptical to conform with the cross section of the deflection device-mounting section.
Further, the deflection device-mounting section of the funnel has a substantially rectangular cross section and the first open end of the deflection device is shaped substantially rectangular to conform with the cross section of the deflection device-mounting section. On the other hand, the correcting coil is shaped elliptical.
According to another aspect of the present invention, there is provided a deflection device for a cathode ray tube, comprising:
a substantially funnel-shaped core having a first open end portion positioned on the side of a phosphor screen of the cathode ray tube and a second open end portion positioned on the side of a neck of the cathode ray tube;
a plurality of deflection coils for deflecting electron beams in horizontal and vertical directions; and
a correcting coil provided at the first open end portion of the core for rotating a displayed image about a tube axis of the cathode ray tube;
wherein the correcting coil is formed non-circular to conform substantially with the first open end portion of the deflection device.
In the deflection device for a cathode ray tube according to the present invention, each of the first open end portion and the correcting coil is formed substantially rectangular or substantially elliptical.
As described above, in each of the cathode ray tube apparatus and the deflection device of the present invention, the correcting coil arranged at the first open end portion for rotating the displayed image about the tube axis is shaped substantially equal to the cross sectional shape of the first open end portion or the deflection device-mounting section of the funnel, making it possible to have the correcting coil positioned close to the tube axis, or the electron beams. It follows that it is possible to correct efficiently the positional deviation of the displayed image by the magnetic field generated from the correcting coil so as to obtain desired displayed image characteristics.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.